非火山地热区玛旁雍热田土壤CO2脱气研究
Soil CO2 degassing process and flux from the Mapamyum non?volcanic geothermal region
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摘要: 提要: 地热活动是地球脱气的重要形式之一, 其过程常伴随大量温室气体排放。选取非火山地热区西藏玛旁雍热田作为研究对象, 基于菲克扩散定律对地热田区土壤CO2脱气量进行评估。结果表明: 该区一般土壤CO2脱气通量为0.167~0.771 kg/(m2·a), 含喷气孔区域土壤CO2脱气通量为2.054~7.877 kg/(m2·a), 含喷气孔地区的土壤CO2脱气通量是一般土壤脱气量的18.9倍; 与全球火山区土壤脱气量(0.001~2.25 Mt/(m2·a))相比, 其值显著偏低; 但比青藏高原高寒草原生态系统土壤的CO2排放量(187.46 g/(m2·a))大。结合区域地质背景推测地热系统中的CO2含量主要来源于岩浆脱气和热液同长石等围岩矿物的蚀变反应。区内土壤CO2的低脱气通量受透水性较差的碎屑岩沉积盖层约束。Abstract: Abstract: Geothermal activity is an important form of earth degassing, which is frequently accompanied by a large number of greenhouse gas emissions. Taking Mapamyum of non?volcanic geothermal region in Tibet as a study case, the authors evaluated the degassing flux of geothermal soil CO2 based on the Fick's law of diffusion. The results indicate that the soil CO2 degassing flux is from 0.167 to 0.771 kg /(m2·a), while the fumarole CO2 degassing flux is from 2.054 to 7.877 kg/(m2·a) which is 18.9 times that of the soil; Compared with global volcanic soil (0.001 ~ 2.25 Mt/(km2·a), the soil CO2 degassing flux is significantly lower in value but larger than the Alpine grassland ecosystem soil CO2 emissions in the Tibetan Plateau (187.46 g(m2 a)?1)). Combined with tectonic setting, the authors evidently hold that CO2 in the geothermal system is mainly derived from magma degassing and hydrothermal fluid with walk rock alterations such as feldspathization. The low zone of soil CO2 degassing flux is constrained by the poor permeability clastic sedimentary cover.
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Keywords:
- soil degassing /
- CO2 flux /
- degassing mechanism /
- non?volcanic region /
- Mapamyum geothermal field
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